Add vue-router, login/setup flow and backend logging

Refactor frontend to route-based navigation with vue-router, add
system setup and login pages with API integration. Add structured
logging, access-log middleware and startup lifecycle to FastAPI
backend.

web/src/composables/useToast.js

@@ -1,13 +1,15 @@
 import { ref } from 'vue'
 
+const toastText = ref('')
+
+function toast(text) {
+  toastText.value = text
+  clearTimeout(toast.timer)
+  toast.timer = setTimeout(() => {
+    toastText.value = ''
+  }, 3200)
+}
+
 export function useToast() {
-  const toastText = ref('')
-
-  function toast(text) {
-    toastText.value = text
-    clearTimeout(toast.timer)
-    toast.timer = setTimeout(() => { toastText.value = '' }, 3200)
-  }
-
   return { toastText, toast }
 }